In the oil and gas exploration and production industry, well boreholes are drilled from surface in order to access subsurface hydrocarbon-bearing formations. A tubular string, such as a completion string, may be run into the borehole and operable to perform a number of different operations in the borehole. One operation which may be carried out in the borehole is hydraulic fracturing, which involves the injection of fluid into the formation to propagate fractures in the formation rock and increase flow of hydrocarbons into the borehole for extraction. In use, one or more fracturing tools may be run into the borehole with the completion string and located adjacent to the formation. Fluid may then be directed through ports in a sidewall of the fracturing tool and injected into the formation. In some instances, a number of fracturing tools may be located at different axially spaced positions in the completion string and configured to facilitate fracturing of multiple and/or selected formation zones.
Completion strings are becoming ever more complex, with the various completion string tools utilising a variety of activation mechanisms, forces and pressures. At the same time, there is a significant drive to improve the effectiveness and reliability of tools which are deployed and operated in a downhole environment, for example to ensure that the tools operate at maximum efficiency, have minimum risk of failure or imprecise operation, can be flexible according to operator requirements, and minimise any necessary remedial action, associated time delays and costs.
In some applications, shifting tools can be used for mechanical actuation of downhole tools. Typically, shifting tools are attached to a work string and can be used during completion of a well to open, close or otherwise shift the position of downhole flow control or circulation devices, such as sliding sleeves. In order to perform a mechanical actuation, the shifting tool is manipulated (via the work string) from surface. Typically, actuation is achieved by locking the shifting tool onto profiles provided on the downhole tools and performing a combination of the following operations: pulling (work string in tension) pushing (work string in compression), jarring or rotating to deliver the necessary force or impact to the tool with which it is engaged.
As will be appreciated, however, it can be difficult to accurately control the operations of the shifting tool especially when it is situated at the end of several kilometers of work string and/or the shifting tool is located in a horizontal or highly deviated wellbore. In these situations it is usually not possible to accurately predict at surface whether the intended actuation has been successful. An additional disadvantage of these conventional shifting tools is the difficulty of use. For example, jarring down or slacking off to cause compression of the work string risks that the work string will ‘catch’ on other downhole tools or land on an unintended component with significant force thereby causing damage.